The temporomandibular joint articulates the mandible (the lower jawbone) to the temporal bone of the skull. If the female and male portions of the temporomandibular joint of an individual are misaligned or if the joint or the interposed disc is damaged or destroyed, pain and altered function may result. One technique used to relieve joint pressure and reposition the members of the joint involves the construction of a splint or a removable intraoral appliance into which the upper and lower teeth fit in such a manner as to realign and reposition the members of the temporomandibular joint in an attempt to relieve joint pressure, provide relaxation of the jaw muscles and allow healing of the joint.
A splint is typically molded from a thermoplastic or thermosetting polymer and contains on its upper and lower surfaces a reverse image or impression of the upper teeth and the lower teeth. Stone models or casts are made from these impressions of the upper and lower teeth. These casts must then be positioned or registered relative to each other so as to achieve a desired relationship in the temporomandibular joint. Traditionally, splints have been made by first taking separate impressions of the upper and lower teeth utilizing conventional techniques. An intraocclusal bite record is then usually made by placing a relatively thin sheet of wax or other bite registration material between the patient's teeth and having the patient bite in the desired jaw relationship. This procedure involves a separate step utilizing the registration material which is subsequently interposed between the dental casts or models of the teeth to align the models in the desired relationship. This conventional step of relating dental casts with a separate interposed bite registration material for the purpose of producing splints, or for other occlusal therapy, introduces inaccuracies because inherent distortion of the wax or other bite registration material, especially from temperature changes, may result in an inaccurate mounting or relationship of the patient'dental casts. The multiple steps involved in handling the separate bite registration material also lead to additional distortion of the relationship between the mounted casts.
Mounting the lower dental cast to the upper cast requires a separate step which is a facebow transfer. A facebow is positioned on the patient's head relative to the axis-orbital plane which relates the location of the upper dental arch to the temporomandibular joint. The facebow is then transferred to an articulator, a machine used to simulate jaw function. The model made from the impression of the upper teeth can then be positioned on the articulator utilizing the facebow. This separate step also introduces the possibility of distortion of the mounting. Thereafter, the model made from the impression of the lower teeth is positioned against the upper model using the intraocclusal bite record. Completion of these separate steps and mounting of the dental casts on the articulator yields a rigid mechanical analog of an individual's jaw movements and relationships.
If, for example, it is desired to make a splint in which the patient's lower jaw is moved two millimeters forward of its normally closed position to relieve pressure on the temporomandibular joint, the model of the lower teeth is moved forward relative to the model of the upper teeth and affixed at the new position. A splint is then produced from the repositioned location of the models of the upper and lower teeth. As one might surmise, this repositioning can introduce several inaccuracies into the splint. As a result, when a splint is fitted to a patient's teeth, a significant amount of time and effort may be required in order to obtain a final accurate relationship of the paired temporomandibular joints and the upper and lower teeth relative to the splint. This same registration technique described herein is applicable to recording jaw positions and relationships for fabrication of removable orthodontic appliances, for relating complete dentures, for mounting dental casts for diagnostic purposes including bite adjustments and for fabrication of single or multiple units of fixed or removable prosthetics.